Hydraulic fracturing is a common technique used to improve production from existing wells, low rate wells, new wells and wells that are no longer producing. Fracturing fluids and fracture propping materials are mixed in specialized equipment then pumped through the wellbore and into the subterranean formation containing the hydrocarbon materials to be produced. Injection of fracturing fluids that carry the propping materials is completed at high pressures sufficient to fracture the subterranean formation. The fracturing fluid carries the propping materials into the fractures. Upon completion of the fluid and proppant injection, the pressure is reduced and the proppant holds the fractures open. The well is then flowed to remove the fracturing fluid from the fractures and formation. Upon removal of sufficient fracturing fluid, production from the well is initiated or resumed utilizing the improved flow through the created fracture system. In some cases, such as recovering natural gas from coal bed methane deposits, proppants are not applied and the simple act of fracturing the formation suffices to provide the desired improvement in production. Failure to remove sufficient fracturing fluid from the formation can block the flow of hydrocarbon and significantly reduce the effectiveness of the placed fracture and production from the well. In order to improve fracture fluid recovery, gases, predominantly nitrogen and carbon dioxide are used in hydraulic fracturing operations.
The use of gases in the fracturing process, particularly carbon dioxide and nitrogen, is common within the industry. By using these gases the liquid component of the fracturing fluid can be reduced or eliminated. With less liquid used in the fracture treatment and the high mobility and expansion of the gas component, the fracturing fluids are much easier to remove. Further, replacement of liquids with gases can provide economic and environmental benefit by reducing the liquid volume needed to complete the fracturing treatment. Generally fracturing compositions using gases can be distinguished as pure gas fracturing (a fluid comprised of nearly 100% gas including carbon dioxide or nitrogen), a mist (a mixture composed of approximately 95% gas (carbon dioxide or nitrogen) carrying a liquid phase), a foam or emulsion (a mixture composed of approximately 50% to 95% gas formed within a continuous liquid phase), or an energized fluid (a mixture composed of approximately 5% to 50% gas in a liquid phase).
The use of nitrogen or carbon dioxide with oil or water based fracturing fluids has been described in the prior art, and can provide a range of benefits. However, in spite of all these benefits, the use of nitrogen or carbon dioxide in fracturing treatments can still have some detrimental effects on the hydraulic fracturing process, create issues during fracture fluid recovery which increase costs and negatively impact the environment.
Other gases have been proposed to gain the benefits attained with adding gases to fracturing fluids while avoiding at least some of the inherent difficulties found with nitrogen and carbon dioxide. Specifically, natural gas has been proposed for use in hydraulic fracturing. Natural gas may be non-damaging to the reservoir rock, inert to the reservoir fluids, recoverable without contamination of the reservoir gas and is often readily available.
However, while the use of natural gas for hydraulic fracturing treatments has been suggested, it is potentially hazardous, and a suitable and safe apparatus and method for hydraulic fracturing using natural gas has not been provided.